Damage Output: Low (max 12)
Threat Range: Medium (9" Charge, 8" with shield)
Profile: Marcus has high AGI for a defender (4), and MOV 4, MEL 6, RES 2 which are average stats. He has 16 boxes which is low for a defender but not low in general. His Soul Harvest of 4 is pretty good.
What does he do?: The main thing Marcus does in charge and knock things down. Though his damage on the shield is quite low and it only has a range of 1" he only needs 1 manoeuvre symbol to knock a model down (plus damage). His protective stance is one of the better defender abilities too, he is able to add a RES to any non-defender model and this can stack with the native RES on the model, abilities on the model, and the Glyph of Warding. Lastly his fate abilities can be pretty useful, the wall in particular can make it very hard to attack a model in melee particularly in conjunction with Marcus' positioning and other models and can provide cover. His level up abilities are situational but can be very strong.
Fate Appetite: Low. He needs fate to drop a wall and to use a blizzard token at level 3. Though these are situationally very strong most turns you can get a very high return from Marcus by using his shield to knock down a model and occasionally using protective stance. The fact that protective stance doesn't use a fate allows you to much more reliably build a synergies around it without worrying about low fate maps or needing rerolls. The wall in my opinion is the stronger of his fate abilities and learning to use it correctly especially in the late game is what make a good Marcus player.
Level Appetite: Low. Winter's bite is one of those abilities that is occasionally clutch but mostly not useful. Blizzard is another one, on rare occassions it is quite useful but often you'll get better use from Marcus just using his base abilities and of course the knock down.
Magic Items: Boots of Agility (Medium). The boots of agility on Marcus really take his survivability up to the next level. He can live without them if you really need another magical item or if he has to use all his movement to get forwards to contest a shrine but they do make a massive difference to his game. He doesn't get a lot of use out of the other items.
Combinations: I like Marcus in a lot of warbands because he doesn't need fate or levels. He works particularly well with Gendris who can use Root on him. He also likes models that can heal. Models that need crits or abilities that require 2S + damage really make good use of his knock down ability. Models with 1 RES or the ability to increase their RES make good use of his Defensive Stance ability, Svetlana really makes excellent use of that ability.
Ban Targets: Bastian. Marcus is really able to get a roll on if he activates after an enemy aggressor has activated, knocks them down and lets your aggressors get in to attack. Bastian gives your opponent a second chance to stand up the model so needs to go. He has trouble knocking down defenders but generally they have low AGI anyway.